1. Field of the Invention
The present invention relates generally to flow control valves, and more particularly, but not by way of limitation, to an improved flow control valve for preventing drainage of drilling fluids from a standpipe and rotary hose of a drilling rig when flow of the drilling fluid through a drill string is interrupted.
2. Discussion of the Prior Art
When drilling oil and gas wells using a rotary drilling rig, drilling fluids are circulated down the drill pipe through the bit and up the outside of the drill pipe. Each time a section of drill pipe is added to the drill string, it is necessary to halt or interrupt the flow of drilling fluids through the drill pipe. In such instances, problems are encountered because of the tendency of the drilling fluid to drain from the standpipe and rotary hose of the rig.
In an effort to resolve this problem, ball valves have been incorporated into the drill string. However, the normal useful life of one such ball valve is approximately 325 closures before the seat of the ball valve must be reworked, an expensive and time consuming procedure. For example, generally the ball valve in a drill string must be reworked or replaced after drilling to a depth of 9,000 feet. That is, 325 connections of drill pipe are required to form the drill string operating at a depth of 9,000 feet, resulting in the ball valve being actuated 325 times (its normal useful life) in order to interrupt the flow of drilling fluid through the drill string during the drilling of the well.
Because of the limited useful life of ball valves, and the expense incurred in reworking or replacing ball valves during the drilling operation, improved valve assemblies have been sought which can effectively prevent the drainage of drilling fluid from the standpipe and rotary hose when the flow of drilling fluid through the drill string is interrupted.
A pressurized check valve which overcomes many of the problems inherent with the use of ball valves in a drill string is disclosed in my U.S. Pat. No. 4,811,758, entitled "Pressurized Check Valve" and issued Mar. 14, 1989. The pressurized check valve disclosed in the '758 patent is a self-contained valve which is automatically actuated in response to fluid flow pressure of drilling fluids injected into the drill string. The pressurized check valve comprises a tubular body member having a valve chamber and a flow restricting assembly supported in the valve chamber. An access bore extends through a side wall of the tubular body member so as to openly communicate with the valve chamber.
The flow restricting assembly, which is secured within the valve chamber, is constructed to automatically open and close the valve chamber in response to the pressure of the fluids flowing through the tubular body member and the flow restricting assembly. The flow restricting assembly includes an elastomeric sleeve defining a bore therethrough which substantially corresponds in diameter to the diameter of a bore of the tubular body member downstream of the valve chamber when the elastomeric sleeve is in a non-compressed state.
A sleeve retention assembly is supported by the tubular body member for securing an upstream end of the elastomeric sleeve such that a medial portion and the downstream end of the elastomeric sleeve are disposed within the valve chamber. The medial portion of the elastomeric sleeve cooperates with the internal wall of the valve chamber to form an annular pressure cavity which openly communicates with the access bore extending through the side wall of the tubular body member. An annular piston supported by the downstream end of the elastomeric sleeve is slidably movable through the valve chamber.
In order to pressurize the annular pressure cavity so that the elastomeric sleeve will remain in a closed position until the flow of fluid therethrough is sufficient to overcome the pressure in the annular pressure cavity and cause the elastomeric sleeve to be displaced to an open position, a loading valve assembly is supported in the access bore so as to seal the access bore while permitting the annular pressure cavity to be charged to a predetermined pressure. The pressurized gas in the annular pressure cavity causes the elastomeric sleeve to restrict or collapse and thereby close the valve chamber to fluid flow until such time as the pressure of fluid injected through the tubular body member is sufficient to overcome the pressure in the annular pressure cavity.
While the pressurized check valve described above is self-contained and automatically actuated in response to flow pressure of drilling fluid injected into the drill string, new and improved flow control valves for incorporation into a drill string are constantly being sought. It is to such an improved flow control valve that the subject invention is directed.